1. Field of the Invention
The present invention relates to a hydroforming method and, more particularly, to a hydroforming method for making hardware and a metal box having approximately right-angled corners.
2. Description of the Related Art
Conventional thin shell metal products are generally made by punching, casting or forging. However, punching, casting, or forging can not easily achieve production of metal products with a specific shape, particularly hardware and metal boxes having a dramatic change in the geometric shape, such as a corner having a small radius, or a circular, elliptic, rectangular, or polygonal shape having a throat in only one side. Thus, in order to increase the appearance variety of the metal products for wide applications in casings for electronic gadgets, such as cell phones, cameras, computer main units, and televisions, or oil tank casings for vehicles, current manufacturers can only choose a milling technique for production.
Taking production of hardware having a rectangular shape by using a conventional milling technique, a metal block is firstly cut to remove redundant material, forming a box-shaped embryo having a predetermined box shape. Then, each corner of the box-shaped embryo is repeatedly milled until each corner approaches the desired special angle (such as a right angle). A metal box having a special angle is, thus, produced.
However, hardware and metal boxes having a special angle produced by the conventional milling technique always lead to excessive material waste due to over cutting of material during the cutting procedure, resulting in a burden to the costs. Furthermore, more tooling processes are required to form the predetermined angle in each corner of the box-shaped embryo by milling, resulting in complex procedures and lack of utility.
Therefore, other manufacturers choose hydroforming to produce hardware and metal boxes having a special angle. Taking sheet metal hydroforming as an example, a liquid pressure is continuously applied to a side of a sheet metal, and a punch of a hydroforming machine pushes the other side of the sheet metal, forcing the sheet metal to tightly abut the outline of the punch under the action of the liquid pressure and gradually shaping the sheet metal into hardware having a special angle as the punch is fed. However, when the corner of the hardware is a special corner with an approximately right angle (a small radius R), the material of the sheet metal can not smoothly flow into each corner due to the excessively small angle of the corner to be formed. This causes gradual thinning at the upper or lower portion of each corner, such that the sheet metal breaks during expansion of the corners, because the remaining material can not be supplied to the corners of the sheet metal and causes thinning at the corners. Furthermore, the shaping method by feeding the punch can not produce hardware and metal boxes having a throat in only one side, either.
Thus, it is necessary to develop a method sufficient to solve the above problems and suitable for producing hardware and metal boxes having various shapes, such that the hardware and the metal boxes can not only have a throat in only one side but can have approximately right-angled corners without thinning and breakage.